Research On Key Techniques Of Downlink Non-orthogonal Multiple Access

The fifth generation cellular system (5G) is a mobile communication network for 2020. The rapid development of mobile Internet and the Internet of Things has become a major driving force for the development of 5G. Non-orthogonal multiple access is not only able to provide high-speed data services, massive connectivity, and also reduce the end-to-end delay without user scheduling. Above all, the new multiple access technology for future 5G is important.First of all, the common downlink power domain and code domain non-orthogonal multiple access technologies are briefly introduced. Then,the advantages, disadvantages, technical difficulties and applicable scenarios are analyzed.Then, this thesis focuses on the user grouping algorithm and power allocation algorithm in downlink non-orthogonal multiple access. Firstly,the restriction of traditional user grouping and power allocation algorithms are analyzed through deep study of downlink multi-user scenario and the scheduling algorithm. Then, a novel multi-user grouping algorithm with low complexity and a power allocation algorithm are proposed. In the multi-user grouping algorithm, we firstly propose a two-user grouping algorithm, and then we extend it to multi-user scene through equivalent user merging. Meanwhile, to ensure the system throughput, a multi-user power allocation algorithm is proposed based on the multi-user grouping algorithm. The multi-user power allocation algorithm could adaptively adjust the number of accessing users according to the channel state information of the grouping users. The power allocation algorithm guarantees the system throughtput, while enhancing the robustness of the system.At last, the pattern division multiple access (PDMA) is studied in this paper. Traditional successive interference cancellation (SIC) receiver is too difficult to guarantee reception performance, and back propagation receiver is not suitable for downlink scenario due to the high complexity.This thesis proposes a scheme based on bit mutual information. The mathematical expressions of the mutual information of each bit of various modulation constellations are given. The simulation results show that the bit error rate of the new scheme is better than that of traditional SIC receiver with a lower complexity, but the data transmission rate of the new scheme is worse than that of the traditional scheme. The transmission rate of the new scheme still needs further research.